Comparative genetic characterization of Listeria monocytogenes isolates from human and animal listeriosis cases

Abstract

Listeria monocytogenes isolates from human sporadic and epidemic cases (n l 119) and from animal cases (n l 76) were characterized by automated ribotyping and PCR-restriction fragment length polymorphism (PCR-RFLP) typing of the virulence genes actA and hly. This combination of typing methods differentiated 39 distinctive strains, each reflecting a unique combination of ribotypes, hly and actA alleles. Simpson's index of discrimination indicated a high discriminatory ability of ribotyping for both animal (0867) and human isolates (0857), which was further increased by the addition of hly and actA typing (0916 and 0904, respectively). Ribotype and hly allele data were further used to group isolates into three genetically distinct lineages. Each lineage is composed of several ribotype fragment subsets, each of which contains multiple ribotypes characterized by common ribotype fragments. To determine whether certain clones of L. monocytogenes show indications for unique pathogenic potential or host specificity, frequency distributions for five genetic characteristics (i.e. lineage, ribotype, ribotype fragment subset and hly and actA allele) were calculated for isolates from animal cases, human epidemic cases and human sporadic cases. Lineage III isolates were found less frequently in human cases (1 of 119 isolates) than in animal cases (8 of 76 isolates ; P l 0003). These results suggest the possibility of host specificity for non-primate mammals among lineage III strains. In addition, lineage I strains were found more frequently among human cases than among animal cases (P T 0001). Among the eight hly alleles observed, hly allele 1 was more common among human isolates as compared to animal isolates (P l 0002). We also identified one ribotype (DUP-1030) which was significantly more common among animal isolates (P l 0005) and one ribotype (DUP-1038 ; lineage I) which was significantly more common among human epidemic isolates as compared to human sporadic isolates (P T 0001). These findings confirm the presence of clonal groups of L. monocytogenes, which appear to be characterized by unique virulence or host specificity patterns. This study also establishes baseline data describing the genetic diversity of human and animal L. monocytogenes isolates which can be utilized in future surveillance programmes to track the emergence of new strains.

Molecular Characterization and Serotyping of Listeria monocytogenes with a Focus on Food Safety and Disease Prevention

“…Isolates in lineage III are known to be more prevalent in animals with clinical Listeriosis (Jeffers et al, 2001). What was also significant was that isolates belonging to division II were not detected; no isolates were positive for PCR using D2 specific primers.…”

Review. Dairy farm management and production practices associated with the presence of Listeria monocytogenes in raw milk and beef

“…Two of these lineages (I and II) cause predominantly human infections, whereas lineages III and IV have never been involved in human disease, being responsible of clinical listeriosis in animals (Jeffers et al, 2001;Nightingale, 2010). The explanation of this finding is unknown, since both lineages share most of known virulence factors.…”

Genetically Related Listeria Monocytogenes Strains Isolated from Lethal Human Cases and Wild Animals

“…In other words, although food is a major source of human infection, not all strains that contaminate food possess a similar virulence potential to cause invasive infection in humans. Analysis of domestic animal and farm environmental isolates revealed that some strains associated with human infection circulate in the agricultural complexes [20]. Although the role of the wild nature as an original source of listerial infection was suggested, the information about clone distribution among L. monocytogenes disseminated in natural ecosystems and their phylogenetic relationships with epidemiologically important clones is scarce [13; 19; 54].…”